This invention relates to receiving arrangements for audio frequency signals transmitted by way of lines of an alternating current (a.c.) distribution network.
Such receiving arrangements may for example be used in installations for the automatic transmission of information to a central answering station, such information being collected by meter condition detecting devices disposed in a low-voltage level of the network. In principle, such a central station may be disposed in the same voltage level of the network as transmitters in the detection devices. Since at least in larger-size networks, the central answering stations are at a higher voltage level of the network, in particular at a medium voltage level, in order to ascertain the maximum number of counter conditions, the signals must transfer the information by way of distribution transformers between the two voltage levels and must be decoupled from the higher network level.
U.S. Pat. No. 4,307,380 describes a receiving arrangement for audio frequency signals wherein a wide-band audio frequency signal is received by coupling to an a.c. distribution network, freed of noise components by a noise filter, and fed to evaluation chains. Such receiving arrangements are intended for a system in which the signal frequency alters within a pulse in a predetermined manner.
U.S. Pat. No. 1,724,112 discloses a system for transmitting information by means of audio frequency signals, over a multi-phase network, wherein as shown in FIG. 7 thereof, signals are decoupled from two phases of the low voltage level, the detected currents going in the opposite direction.
Finally, G.B. Pat. No. 1,322,461 discloses a ripple control process with wide-band signal transmission (signal spectrum of up to several hundred Hz) by way of lines of an a.c. distribution network, by the pulsed superimposition of audio frequency oscillations. The length of the superimposed pulses is within a range which is defined by an eighth of a period and a full period of the network a.c. voltage. The associated receiver uses a high pass filter, with a comb filter disposed downstream thereof, for filtering out harmonics of the network voltage.
In the previously known procedure for decoupling audio frequency signals to be evaluated from any network voltage level, the arrangement used a transformer together with filters, which requires a considerable amount of expenditures on technical equipment and tuning operations.
According to the invention there is provided a receiving arrangement for audio frequency signals transmitted by way of lines of an alternating current distribution network, wherein a receiver is connected by means of at least one signal transformer to a secondary circuit of at least one transformer which is provided in the alternating current distribution network, and the signal transformer is formed as a high-pass filter.
A preferred receiving arrangement embodying the invention and described hereinbelow has the advantage that the receiver is of a simple design and that conventional economical individual components can be used for the signal decoupling action and a signal transformer which is required in any case, such components permitting a double function without additional expensive passive filter components which occupy a large amount of space. Some individual components can also be used for other purposes, thereby making savings on technical equipment. Finally, the preferred arrangement is preferably suitable for the above-mentioned wide-band signal transmission system of U.S. Pat. No. 4,307,380.
The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings.